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Journal of Bacteriology, June 2009, p. 3492-3503, Vol. 191, No. 11
0021-9193/09/$08.00+0 doi:10.1128/JB.00119-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Pseudomonas aeruginosa Rugose Small-Colony Variants Have Adaptations That Likely Promote Persistence in the Cystic Fibrosis Lung
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Melissa Starkey,1,
Jason H. Hickman,1
Luyan Ma,2
Niu Zhang,3
Susan De Long,4
Aaron Hinz,5
Sergio Palacios,1,
Colin Manoil,5
Mary Jo Kirisits,4
Timothy D. Starner,3
Daniel J. Wozniak,2
Caroline S. Harwood,1 and
Matthew R. Parsek1*
Department of Microbiology, University of Washington, Seattle, Washington 98195-7242,1 Infectious Disease, Microbiology, Center for Microbial Interface Biology, The Ohio State University, 460 West 12th Avenue, Columbus, Ohio 43210,2 Department of Pediatrics, College of Medicine, 2633 Carver Pavilion, University of Iowa, Iowa City, Iowa 52242,3 Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin, 1 University Station C1786, Austin, Texas 78712-02873,4 Department of Genome Sciences, University of Washington, Foege Building S-250, Box 355065, 1705 NE Pacific St., Seattle, Washington 98195-50655
Received 28 January 2009/ Accepted 18 March 2009
Pseudomonas aeruginosa is recognized for its ability to colonize diverse habitats, ranging from soil to immunocompromised people. The formation of surface-associated communities called biofilms is one factor thought to enhance colonization and persistence in these diverse environments. Another factor is the ability of P. aeruginosa to diversify genetically, generating phenotypically distinct subpopulations. One manifestation of diversification is the appearance of colony morphology variants on solid medium. Both laboratory biofilm growth and chronic cystic fibrosis (CF) airway infections produce rugose small-colony variants (RSCVs) characterized by wrinkled, small colonies and an elevated capacity to form biofilms. Previous reports vary on the characteristics attributable to RSCVs. Here we report a detailed comparison of clonally related wild-type and RSCV strains isolated from both CF sputum and laboratory biofilm cultures. The clinical RSCV had many characteristics in common with biofilm RSCVs. Transcriptional profiling and Biolog phenotypic analysis revealed that RSCVs display increased expression of the pel and psl polysaccharide gene clusters, decreased expression of motility functions, and a defect in growth on some amino acid and tricarboxylic acid cycle intermediates as sole carbon sources. RSCVs also elicited a reduced chemokine response from polarized airway epithelium cells compared to wild-type strains. A common feature of all RSCVs analyzed in this study is increased levels of the intracellular signaling molecule cyclic di-GMP (c-di-GMP). To assess the global transcriptional effects of elevated c-di-GMP levels, we engineered an RSCV strain that had elevated c-di-GMP levels but did not autoaggregate. Our results showed that about 50 genes are differentially expressed in response to elevated intracellular c-di-GMP levels. Among these genes are the pel and psl genes, which are upregulated, and flagellum and pilus genes, which are downregulated. RSCV traits such as increased exopolysaccharide production leading to antibiotic tolerance, altered metabolism, and reduced immunogenicity may contribute to increased persistence in biofilms and in the airways of CF lungs.
* Corresponding author. Mailing address: Department of Microbiology, University of Washington, Box 357242, Seattle, WA 98195-7242. Phone: (206) 221-7871. Fax: (206) 543-8297. E-mail: parsem{at}u.washington.edu
Published ahead of print on 27 March 2009.
Supplemental material for this article may be found at http://jb.asm.org/.
Present address: Department of Surgery, Harvard Medical School, Massachusetts General Hospital, Boston, MA 02114.
Deceased.
Journal of Bacteriology, June 2009, p. 3492-3503, Vol. 191, No. 11
0021-9193/09/$08.00+0 doi:10.1128/JB.00119-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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